The prior art relating to auxiliary locking devices for door locks to insure unauthorized use of the same pertinent to the present invention is generally typified in U.S. Pat. Nos. 1,206,601, 1,917,973 and 2,883,849.
Each of these patents disclose a base plate secured about the keyhole to be protected with a hole provided therein aligned with the same and a cover plate pivotally or slidingly co-operating with the base plate to cover the keyhole and means locking the said plates to one another. The keyhole is thereby covered and cannot readily be tampered with.